Gray was expected to be among the first players chosen in the 2013 MLB Draft, and was considered by the Houston Astros, who had the first overall pick. The Colorado Rockies eventually picked him with the third pick. Gray signed with the Rockies, receiving a $4.8 million signing bonus, which was below the recommended slot value for the pick. Gray made his professional debut with the Grand Junction Rockies of the Rookie-levelPioneer League in July, before receiving a promotion to the Modesto Nuts of the Class A-AdvancedCalifornia League later in the month. For Modesto, Gray pitched to a 0.75 ERA with 36 strikeouts in 24 innings. The Rockies invited Gray to spring training in 2014. They assigned him to the Tulsa Drillers of the Class AATexas League for the 2014 season. He pitched to a 10–5 record, a 3.91 ERA, and 113 strikeouts in innings. He missed the first round of the Texas League playoffs due to a tired shoulder. The Rockies invited Gray to spring training in 2015. They assigned him to the Albuquerque Isotopes of the Class AAAPacific Coast League to start the 2015 season. Gray pitched to a 6–6 win-loss record with a 4.33 ERA and 110 strikeouts in 21 games, including a 2.70 ERA in his last six starts.
Colorado Rockies
Gray made his major league debut with the Rockies on August 4, 2015. Focusing on his fastball and slider, Gray pitched to a 0–2 record and a 5.53 ERA in nine starts for the Rockies. During the 2015–16 offseason, Gray worked to add a curveball. Gray missed the beginning of the 2016 season due to a strained abdominal muscle. On May 13, Gray earned his first career major league win in a 5–2 victory over the New York Mets. He finished the 2016 season with a 10–10 record, a 4.61 ERA, and 185 strikeouts in 168 innings pitched. In 2017, the Rockies named Gray their Opening Day starting pitcher. He went on the disabled list in April with a stress fracture in his left foot. On July 5, Gray hit his first career home run off of Cincinnati Reds pitcher Scott Feldman, which measured. Gray finished the season winning 10 games in 20 starts and a 3.67 ERA. Gray began the 2018 season with a 5.77 ERA in his first 17 starts. On June 20, 2018, he was optioned to Triple-A Albuquerque. He was recalled on July 13. Gray ended the regular season with a 5.12 ERA and 27 home runs allowed. The Rockies did not include Gray on their postseason roster for the 2018 National League Division Series. In 2019, Gray was 11-8 in 25 starts, missing time due to injury.
Personal life
Gray is married. His grandfather was Cherokee, and Gray is a citizen of the Cherokee Nation. His brother, Jack, played linebacker at Northeastern State University. His sister, Brooke, is an aspiring softball player who wants to play for the University of Oklahoma. Since he was 10 years old, Gray has been interested in ghosts and he uses equipment for ghost hunting in hotels.